The subject matter disclosed herein relates generally to imaging systems and techniques, and more particularly to reduction of the effect of dark current, for example.
In certain types of imaging devices, such as positron emission tomography (PET) scanners, arrays of detector elements are used to detect radiation emanating from the patient. In a PET scanner, for example, arrays of scintillator crystals may be used to detect annihilation photons which are generated inside the patient. The annihilation photons are produced when a positron emitted from a radiopharmaceutical injected into the patient collides with an electron causing an annihilation event. The scintillator crystals receive the annihilation photons and generate light photons in response to the annihilation photons, with the light photons emitted to a photosensor configured to convert the light energy from the light photons to electrical energy used to reconstruct an image.
Timing resolution of a time of flight (TOF) PET detector may depend on a number of components, including scintillation crystals and photosensors, and how the scintillation crystals and photosensors are combined into a detector along with readout electronics. Factors relating to the combination of the scintillation crystals and photosensors that may affect timing resolution include, for example, the light sharing scheme among the crystals and photosensors, the layout of photosensors, transit time spread between the photosensors, signal trace layout on amplifier board, and electronics noise, for example.
Because of the high speeds of photons (e.g., the speed of light) and relatively short distances traveled by the photons during imaging, the timing resolution of detectors is critical to imaging. This is even more so as demands for higher resolution increase. For example, in order to achieve sub-250 picosecond (ps) timing resolution with currently available lutetium based scintillators and silicon photomultipliers (SiPM's), direct coupling between a crystal array and a SiPM array may be achieved with a layer of optical glue or a relatively thin lightguide. In some instances a beveled lightguide may be employed; however, for example, timing for crystals located at a beveled edge may be degraded. Further, direct coupling may require optimization for various timing parameters, such as light collection, light spread, dark current, or fast rising edge of the signal, among others.